Photoisomerization of alpha,alpha&#39;-dimethylmuconic acid



United States Patent 3,497,435 PHOTOISOMERIZATION 0F a,oc'-DIMETHYL-MUCONIC ACID William W. Wimer, East Marlborough Township, ChesterCounty, and George Suld, Springfield, Pa., assignors to Sun Oil Company,Philadelphia, Pa., a corporation of New Jersey No Drawing. Filed May 27,1968, Ser. No. 732,080 Int. Cl. B01t 1/10 US. Cl. 204158 17 ClaimsABSTRACT OF THE DISCLOSURE The trans,trans-isomer of dimethylmuconicacid (DMMA) can be prepared conveniently and in high yields by thephotoisomerization of cis,cis-DMMA 'by using a photosensitizer selectedfrom aromatic hydrocarbons or ketones having triplet state excitationenergy of above 55 kcaL/mole and an oxygenated organic solventcontaining Water. For example, 20 grams of cis,cis- DMMA was slurried inan ethanol/water solvent 1) and heated to reflux in the presence ofincandescent flood lamps and 21.5 grams of benzophenone for 17 hours togive a yield of 71.0 of trans,trans-DMMA. A similar run with thephotosensitizer omitted yield no trans,trans- DMMA.

The present invention relates to a novel process for the isomerizationof 0t,oc' dimethylmuconic acid (DMMA). More particularly it is aphotoisomerization process for converting a,a-dimethyl-cis,cis-muconicacid to the -trans,trans-form thereof. There are three geometric isomersof a,a'dimethylmuconic acid.

or,a'-dimethyl-cis,cis-muconic acid CH3 H C=C CH:

H COzI-I a,a'-dimethyl-cis,trans-mucnoic acid C 02H H C=C C CH3 C=C HCOzH mod-dimethyl-trans,trans-muconic acid The three isomericdimethylmuconic acids are white "ice crystalline powders with thefollowing physical properties:

TABLE I CiS,ciS Cis,trans Trans,trans Molecular Wt 170. 2 170. 2 170. 2Melting pt. C 1 223-224 l 179180 1 332-333 Ionization constants:

1 M.P. varies with the rate of heating. 2 At O. 3 Not determined.

The -cis,cis-DMMA has been produced by two principal methods. The oldermethod is that shown by Elvidge et al., J. Chem. Soc., 1952, pp. 1026-33which is the peracetic acid oxidation of p-xylenol. An alternativemethod for producing the a,a'-dimethyl-cis,cis muconic acid is disclosedin copending commonly assigned application Ser. No. 509,621, Raymond etal., filed Nov. 24, 1965, now Patent No. 3,383,289, which discloses amicrobiological oxidation of alkylbenzenes. The cis,cis- DMMA isproduced by a particular strain or microorganism of genus Nocardia, moreparticularly Nocardia corallina, a culture of which has been depositedwith the American Type Culture Collection, Washington, D.C., under thenumber ATCC 19,070.

In order to obtain the cis,transand the trans-transisomers it isnecessary to isomerize the cis,cis-DMMA. Elvidge et al. inverted thecis,cis-DMMA to trans,trans- DMMA with boiling alkali and tocis,trans-DMMA by conversion to an unsaturated gamma lactonic acid andsubsequent treatment with methanolic sodium mcthoxide.

DMMA can be used for the preparation of polymers such as polyesters andpolyamides or crosslinked with itself to produce a resin. The isomers,particularly the trans,trans-DMMA, have been found to be usefulstabilizers for ot,0l6fi11 polymers such as polypropylene for petroleumWaxes, mineral oils and natural and synthetic rubber.

Briefly stated, the invention is a process of convertinga,u'-dimethyl-cis,cis-muconic acid to a,ot'-dimethyl-trans,trans-muconic acid comprising contacting a,a'-dimethylcis,cis-muconicacid with an inert oxygenated organic solvent and water at a temperaturein the range of 30 to 200 C., subjecting the resulting mixture to lightin the presence of a photosensitizer selected from the group consistingof aromatic ketones, aromatic hydrocarbons and mixtures thereof havingtriplet state excitation energy of above 55 kcal./mole and recoveringm,a'dimethyltrans,trans-muconic acid.

One embodiment of the present invention is a one-stage process for theconversion of a,a'-dimethyl-cis,cis-muconic acid toa,u'-dimethyl-trans,trans-muconic acid comprising contactinga,a-dimethyl-cis,cis-muconic acid with an inert oxygenated organicsolvent and Water in the presence of a photosensitizer selected from thegroup consisting of aromatic ketones, hydrocarbons and mixtures thereofhaving triplet state excitation energy of about 55 kcaL/mole and lightat a temperature in the range of 30 to 200 C. and recoveringor,'-dimethyl-trans,trans-muconic acid.

In another embodiment the cis,cis-DMMA is converted to cis,trans-DMMA inone step and then in another step by the addition of the photosensitizerthe cis,trans-DMMA is converted to trans,trans-DMMA. Briefly stated thisprocess comprises the steps of (1) contactinga,a-dimethyl-cis,cis-muconic acid with an inert oxygenated organicsolvent and Water at a temperature of 30 to 200 C. (2) adding aphotosensitizer selected from the group consisting of aromatic ketones,aromatic hydrocarbons and mixtures thereof having triplet stateexcitation energy above 55 kcal./mole to the mixture of step 1 andsubjecting the mixture to light at a temperature in the range of 30 to200 C. and recovering a,a'-dirnethyl-trans,transmuconic acid.

The presence of both a photosensitizer and water have been found to benecessary to obtain high conversions in reasonable periods of time. Thewater is preferably present as part of the solvent, and is presentgenerally in the volume ratio of inert oxygenated organic solvent toWater in the range of 100:1 to 1:1 though the preferred ratio is in therange of 20:1 to 4:1.

The omission of water from the system will result in substantially loweryields and longer conversion times. The entire function of water is notknown but it is known to be important for rapid conversions ofcis,cis-DMMA to cis,trans-DMMA. The inert oxygenated organic solvent ispreferably selected from the group consisting of primary alcohols,tertiary alcohols, glycols, glycol ethers, lower ketones and mixturesthereof, for example, methanol, ethanol, n-propanol, ethylene glycol,propylene glycol, diethylene glycol, 2-methoxy-ethanol, 2-ethoxy-ethanoland ketones having 3-7 carbon atoms such as acetone, methylethylketone,diethyl ketone and the like. The preferred inert oxygenated organicsolvent is an alcohol selected from the group consisting of methanol,ethanol, and npropanol.

One' of the advantages of the described solvents is the relationship ofthe solubilities of the isomers in each. The trans,trans-DMMA has beenfound to be the least soluble of the isomers in any particular solventof the type described, although the actual solubilities will vary. Thenet result is that the trans,trans-DMMA can be precipitated in highpurity from the reaction medium while any residual cis-cisandcis,trans-DMMA remains in solution.

The photosensitizer is an aromatic ketone or an aromatic hydrocarbonhaving a triplet state excitation energy of about 55 kcal./mole. Themore advantageous photosensitizers which are preferred will be thosehaving triplet state excitation energies in the range of 55 to 80 kcal./mole.

The efiiciency of photosensitizers for the conversion of cis,cis-DMMA totrans,trans-DMMA varies depending on their molecular structure. As seenfrom Tables II, III and V, benzophenone is the most eflicientsensitizer, however, acetophenone, fluorene and phenanthrene also givegood results. Naphthalene and biphenyl are correspondingly less active.Other compounds useful as the sensitizers for the abovephotoisomerization are xanthen-9-one, thioxanthenone, and triphenylene.The photosensitizer is generally employed in approximately equal molarquantities with the charge DMMA present, however, suitable results canbe obtained when the molar ratio of photosensitizer to DMMA to beconverted is in the range of 2:1 to 0.05:1 (Table H).

The light employed can be sunlight, that derived from ordinaryincandescent lamps, flood lamps using tungsten or mercury vaporfilaments, fluorescent lamps, ultraviolet lights and the like. Suitablelight has wave length in the range of about 150-800 m If desired,optical filters transmitting light with the wavelength absorbed only bythe photosensitizer but not DMMA, may be used. It has been convenient touse flood lamps since it was possible to obtain the necessary heat forthe reaction from the light source. Various combinations of the lightsources can be employed together, for example, when ultraviolet light isemployed in addition to flood lamps shorter reaction times are achieved.It should be understood that the light can be a part of the spectrumsuch as ultraviolet, i.e., 200-400 m or can be a broader spectrum of allthe the Wave lengths in the range of 150-800 mg.

In a typical run, 20 ml. of water is added to 200 ml. of ethanol. Enoughcis,cis-DMMA is added to produce a slurry at room temperature (25 C.).An equal molar amount of benzophenone based on cis,cis-isomer is addedto the slurry and the reaction mixture heated to reflux by three GeneralElectric 150 watt flood lamps. The temperature for the process of theinvention can be in the range of 30 to 200 C. but it is preferably inthe range of 60 to 120 C. Depending on the amount of cis,cis-DMMAcharged originally, either a complete solution is obtained at the refluxtemperature or a gradual dissolution of the starting material will occurin the course of the reaction. If a complete solution is not obtained atthe reflux temperature, refluxing is continued for about 34 hours. Ifthe cis,cis-DMMA goes into solution at reflux temperature, refluxing iscontinued until appreciable quantities of precipitate appear in therefluxing solvent. The precipitate is trans,trans-DMMA, which has a verylow solubility in ethanol (0.39 g./ g.). The cis,cis-DMMA is also poorlysoluble in ethanol, (3.30 g./ 100 g.) but this is about 10 times moresoluble than the trans,trans-isomer, thus making separation and recoveryof the trans,trans-isomer very easy. The trans,trans-DMMA is recoveredby filtering and can be washed with water and ethanol to remove anycis,cis-DMMA, cis,trans-DMMA or benzophenone.

The cis,trans-isomer is an intermediate product of the isomerization.For example, if cis,cis-DMMA is heated for about 10 hours in theethanol-Water solvent in the absence of benzophenone high yields ofcis,trans-DMMA are achieved. The cis,trans-DMMA can be recovered andpurified and subsequently converted to trans,trans-isomer or it can beconverted directly to the trans,trans-isomer by addition of benzophenoneand irradiation of the solution containing the cis,trans-DMMA (TableII). The cis,transisomer is also useful for the preparation of polymersand the like.

If the light source is located outside of the reaction zone, the reactormust be sufliciently transparent to allow adequate light to pass intothe reaction solution to achieve the conversion. Suitable materials areglass, for example, Pyrex and quartz, crosslinked polymers, and thelike. The reaction vessel may be made of any conventional material ifthe light source is located inside the reactor, for example, stainlesssteel, refractory ceramics and the like.

The following examples are submitted to illustrate the variouspermutations and embodiments of the invention.

EXAMPLES 1-12 The equipment consisted of three 15 0 watt flood lamps(General Electric flood 150 Watt, volt) placed at three equidistantpoints around a 500 ml. Erlenmeyer Pyrex flask about an inch from theoutside surface. The flask was equipped with a reflux condenser andstirred by means of a magnetic stirring bar. The flood lamps heated thereaction mixture and maintained it at reflux temperature. Table H showsthe results of 12 runs. Examples 8 and 9 show the effect of omittingbenzophenone. Example 10 shows the effect of omitting water. The resultin both instances is the absence of trans, trans-DDMA in the reactionmixture. Example 12 shows the effect of the addition of an ultravioletsource (Hanovia high pressure quartz mercury lamp, type 16200) to thethree flood lamps. Also a 500 ml. quartz round bottom flask wassubstituted. The net eflect was to substantially reduce the reactiontime. Note that at two hours 38% yield was achieved in Example 12compared to 10% yield after 6 two hours in Example 4 where noultraviolet light was Other analytical methods employed, were paperemployed. chromatography and nuclear magnetic resonance Productidentification and purity in the examples were (n.m.r.).

TABLE II.BENZOPHENONE SENSIIIZED PHOTOISOMERIZATION OF m,m-DIME'IHYLcis,cis MUCONIO ACID TO m,m DIMETHYL trans,trans MUOONIC ACID ChargedRecovery Trans, Cls,cis Benzo- Heating trans DMMA, Ethanol, Water,phenone, time, DMMA, Yield, grams 1111. ml. grams Irradiatlng hoursgrams percent Run N0..

1st crop 26 16. 3 81. 5 2 2 0 1 0 0 2 5 2nd p 16 6 0 Total- 42 16. 9 845 1st crop 14. 2 71. 0 3 20. 0 0 5 2nd D 16 4 0 Total. 41 16. 6 83. 0

34 1s. 0 so 1st. crop 7 5. 3 26. 5 2nd crop 7 4. 4 22. 0 3rd crop 9 3. 618. 0 13 20. 0 200 20 6. 0 4th crop 7 1. 3 6. 5 5th crop 7 0. 8 4. 0

Total. 37 15.4 77. 0

1 (U.V. Lamp in addition to regular flood lamps in Run 12). 2 After 17hours, benzophenone was added.

EXAMPLE 13 This example was performed to show the recycle of thealcohol-water solvent containing benzophenone. After the completion ofthe run of Example 6 the liquid phase was removed by filtration. Thisfiltrate was used in three determined mainly by gas-liquidchromatography (g.1.c.) and by melting point. The g.l.c. methodconsisted of preparing the silyl esters of DMMA usingbis(trimethylsilyl) acetamide (BSA) as the silylation agent. Thisreagent and method are discussed in a paper by J. F. Klebe, H. additiona1 runs with no addition of elther water or benzoig gg and Whlte Chem3390 phenone. The results are set out in Table III. The overall yieldfrom the recycles was about 90% of trans,trans- DMMA.

TABLE III.-RECYCLE OF THE SOLVENT SOLUTION IN THE BENZOPHENONE SENSI-TIZED PHOTOISOMERIZATION OF a,vz-DIMETHYL cis,cis MUCONIO ACID TO 01,07-DIMEIHYL trans,traus MUCONIC ACID Charged Recovery trans Benzo- Heatingtrans Ethanol? Vi'ater, plienoue, time, DMMA 1111. ml. grams Irradiatinghours gram Cis,cis-DMMA, grams 16.3 200 20 21. 5 1st recycle 7 6- 76.0.. 200 20 21. 5 2nd recycle- 6 5. 6 6.0- 200 20 21. 5 3rd recycle 2312. 0 2nd crop, 3rd recycl 17 2. 8

28.3 Total 53 27. 1

1 Amount originally present. 2 Small amounts of ethanol added after eachrecycle to bring to original volume.

7 EXAMPLE 14 EXAMPLE 15 This example shows the production ofcis,trans-DMMA and the subsequent treatment of aliquots thereof. Aslurry of 69 grams of cis,cis-DMMA was heated under reflux in ethanoland water (276 g. each) for 15 hours. The conversion to cis,trans-DMMAis essentially complete. If only ethanol is used the conversion is veryslow. The resulting solution of cis,trans-DMMA Was divided into 4aliquots and treated as indicated in Table IV. Aliquots A-C weresubjected to fluorescent lights by the procedure described in Example 14for about 2 hours. The results are shown in Table IV. The run withbenzophenone gave the best yield of trans,trans-DMMA.

photosensitizer selected from the group consisting of aromatic ketones,aromatic hydrocarbons and mixtures thereof having triplet stateexcitation energy of above 55 kcal./ mole and recoveringa,a'-dimethyl-trans,trans-muconic acid.

2. The process according to claim 1 wherein the volume ratio of inertoxygenated organic solvent to water is in the range of 100:1 to 1:1.

3. The process according to claim 2 wherein the ratio is in the range of20:1 to 4: 1.

4. The process according to claim 2 wherein the molar ratio ofphotosensitizer to dimethylmuconic acid charge is in the range of 2:1 to0.05: 1.

5. The process according to claim 4 wherein the inert oxygenated organicsolvent is selected from the group consisting of primary alcoholstertiary alcohols, glycols, glycol ethers, lower ketones and mixturesthereof.

6. The process according to claim 5 wherein the inert oxygenated organicsolvent is selected from the group consisting of methanol, ethanol andn-propanol.

7. The process according to claim 6 wherein the photo sensitizer isbenzophenone.

8. The process according to claim 7 wherein the volume ratio of alcoholto water is in the range of 20:1 to 4: 1.

TABLE IV.PHOTOISOMERIZATION OF a,a-DIM'ETHYL cis,trans MUCONIC ACID TO01,04- DIMETHYL trans,trans MUCONIC ACID Theoretical amount of Ethanolc,t-DMMA.

water in aliquot Trans, solution assuming 100 a trans- Percentcontaining conversion from Heating DMMA yield t-DMMA, 0,0-DMMA,Additive, time, product, of t,t Aliquot grams grams grams Irradiatinghours grams DMMA A 68. 5 7, 60 0.9 benzophenone- 1st crop 97 5. 2 68. 42nd crop- 17 1. 0 13. 2 3rd crop 86 0. 3 3. 8

Total... 200 6. 5 86.4

a: B 218. 7 24. None 1st crop 97 6.8 28.0 2nd crop 17 4. 2 17. 2 3rdcrop 86 5. 2 21. 4

Total- 200 16. 2 66. 6

C 248.2 27. 55 Trace of iodine 1st crop 97 5. 9 21. 3 17 3. 4 12. 3 866. 2 22. 4

Total- 200 16. 5 56. 0

D Control Not subjected to light 200 Only a trace of solids present 1 INot identified.

EXAMPLES 1640 9. The process according to claim 5 wherein the photo-Using essentially the same procedure and equipment as in Examples 1-12,the photoisomerization of cis,cis- D MMA was carried out with severaldifierent photosensitizers. The results are shown in Table V.

sensitizer is selected from the group consisting of benzophenone,acetophenone, fluorene, phenanthrene, naphthalene, biphenyl,xanthen-9-one, thioxanthenone and triphenylene.

TABLE V.PHOTOISOMERIZATION OF a,-a'-DIMETHYL cis,cis MUCONIC ACID TDIMETHYL trans,trans MUCONIC ACID WITH VARIOUS PHOTOSENSITIZERS Theinvention claimed is:

1. A process for the production of u, x'-dimethyl-trans, trans-muconicacid comprising contacting a,ot'-dimethylcis,cis-muconic acid with aninert oxygenated solvent and water at a temperature in the. range of 30to 200 C., sub- 10. The process according to claim 9 wherein thephotosensitizer is selected from the group consisting of benzophenone,acetophenone, fluorene, phenanthrene, napth alene and biphenyl.

11. The process according to claim 10 wherein the jecting the resultingmixture to light in the presence of a photosensitizer is selected fromthe group consisting of benzophenone, acetophenone, fiuorene andphenanthrene.

12. The process according to claim wherein the temperature is in therange of 60120 C.

13. The process according to claim 1 wherein the light has wave lengthin the range of 150800 mp.

14. The process according to claim 1 comprising the steps (1) contactinga,a'-dimethyl-cis,cis-muconic acid with an inert oxygenated organicsolvent and water at a temperature in the range of 30 to 200 C. (2)adding a photosensitizer selected from the group consisting of aromaticketones, aromatic hydrocarbons, and mixtures thereof having tripletstate excitation energy of above 55 kcal./mole to the mixture of step 1and subjecting the mixture to light at a temperature in the range of 30to 200 C. and (3) recovering a,a'-dimethyl-trans,trans-muconic acid.

15. The process according to claim 14 wherein the inert oxygenatedorganic solvent is selected from the group consisting of methanol,ethanol and n-pr0panol, the volume ratio of the inert oxygenated organicsolvent to water is in the range of 20:1 to 4:1, the photosensitizer isbenzophenone, the molar ratio of benzophenone to dimethylmuconic acidcharge is in the range of 2:1 to 0.05: 1, and the temperature is in therange of 60-l20 C.

16. A process for the production of a,u-dimethyl-trans,- trans-muconicacid comprising contacting a,m-dimethy1- cis,trans-muconic acid with aninert oxygenated solvent and water at a temperature in the range of to200 C., subjecting the resulting mixture to light in the presence of aphotosensitizer selected from the group consisting of aromatic ketones,aromatic hydrocarbons, and mixtures thereof having triplet stateexcitation energy of above kcaL/mole and recovering cn'-dimethy1-trans,trans-muconic acid.

17. The process according to claim 16 wherein the inert oxygenatedorganic solvent is selected from the group consisting of methanol,ethanol and n-propanol, the volume ratio of inert oxygenated solvent towater is in the range of 20:1 to 4:1, the photosensitizer isbenzophenone, the molar ratio of benzophenone to dimethylmuconic acidcharge is in the range of 2:1 to 0.05:1, and the temperature is in therange of 120 C.

References Cited UNITED STATES PATENTS 2,979,445 4/1961 Lanigne et a1.204-458 HOWARD S. WILLIAMS, Primary Examiner

